1. Field of the Invention
The present invention relates to a sign recognition device for recognizing road signs during travel of a vehicle and presenting them to the driver of the vehicle.
2. Description of Related Art
A conventional sign recognition device recognizes road signs from an image captured with a vehicle-mounted camera during travel of a vehicle and produces a screen display of the recognized road signs on a car navigation apparatus to notify them to the driver of the vehicle. For example, according to “Display device for displaying road signs and so on, and method of displaying an image, such as road signs” disclosed by a Japanese patent application (JP, 2005-4410,A), road signs are recognized from an image captured with a vehicle-mounted camera and a screen display of the road signs is produced on a car navigation apparatus, and, when the traveled distance from the recognized position of a recognized road sign exceeds a designated value, when the time which has elapsed since the time at which the road sign was recognized exceeds a designated value, or when receiving an instruction from the driver, the screen display is ended.
Conventional sign recognition devices are constructed as mentioned above, and determine the effective range of each road sign which they have recognized from the traveled distance or elapsed time and switches between display and non-display of each road sign on a car navigation apparatus according to a result of the determination. Therefore, in a case in which either an effective time period or vehicle type is specified with an auxiliary sign, in a case in which there is an advance warning sign showing a specified point existing forwardly, such as a sharp bend or lane warning sign, or the like, these signs are not taken into consideration. A problem is therefore that the effective range of a road sign cannot be determined correctly. Furthermore, because the effective range of a road sign is defined by the number of road sections, instead of the distance from the position of the road sign, the effective range of a road sign cannot be correctly determined by using a conventional method. A further problem is that when the vehicle makes a right or left turn and then deviates from a continuous road section, the effective range of the recognized road sign cannot be correctly determined because the vehicle also deviates from the effective range of the recognized road sign.